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Blowing hot and cold - the off-throttle diffuser debate 15 Jun 2011

Red Bull RB7 - revised blown exhausts Red Bull Racing RB7 diffuser detail.
Formula One World Championship, Rd 3, Chinese Grand Prix, Practice Day, Shanghai, China, Friday, 15 April 2011 McLaren MP4/26 rear floor and exhaust exit detail.
Formula One World Championship, Rd 7, Canadian Grand Prix, Qualifying Day, Montreal, Canada, Saturday, 11 June 2011 Lotus Renault GP R31 diffuser detail. 
Formula One World Championship, Rd 3, Chinese Grand Prix, Practice Day, Shanghai, China, Friday, 15 April 2011 Ferrari 150 Italia rear floor and exhaust exit detail.
Formula One World Championship, Rd 7, Canadian Grand Prix, Preparations, Montreal, Canada, Thursday, 9 June 2011 Red Bull Racing RB7 rear floor detail.
Formula One World Championship, Rd 7, Canadian Grand Prix, Qualifying Day, Montreal, Canada, Saturday, 11 June 2011

Under the banner of Formula One’s Technical Working Group, the teams and the FIA are due to meet on Thursday to discuss the use of blown diffusers, and in particular the expected clampdown on off-throttle blown diffusers, a technology that has become an increasingly hot topic of debate in 2011. Here is our layman’s guide to what is involved…

What is a blown diffuser?
On road cars, the engine exhaust exits are normally located at the rear of the car. On a Formula One car they are deliberately located in front of the rear wheels so that the hot, fast flowing exhaust gases can be channelled towards the car’s rear diffuser. This increases airflow through the diffuser and in turn increases the amount of downforce the diffuser produces. This is perfectly legal under current F1 regulations.

What is an off-throttle blown diffuser?
Normally the engine will only produce exhaust gases when the driver is on the throttle. This means when the driver lifts off, the blown diffuser is suddenly robbed of the additional airflow. To get around this, some teams have modified their engine mapping so that when the driver lifts off, although fuel supply and ignition are cut, airflow through the exhaust - and hence to the diffuser -continues. This technique has become known as ‘cold blowing’ - the exhaust is still ‘blowing’ into the diffuser, but that airflow is now ‘cold’ since no fuel or ignition is involved.

What is ‘hot blowing’?
Some teams have taken things a step further. To make the off-throttle ‘blowing’ as similar - ie as hot and fast flowing - to the on-throttle ‘blowing’ as possible, they cut the ignition when the driver lifts off the throttle, but continue to inject some fuel through the engine’s valves into the exhaust. This fuel ignites on the hot exhaust, increasing the amount, speed and temperature of the airflow exiting towards the diffuser.

Why does the FIA want to clampdown on off-throttle blown diffusers?
The FIA has argued that the car’s exhaust system is there to exhaust gasses from the engine. It doesn’t do that when a driver is off the throttle and teams are now using it to instead influence the aerodynamic characteristics of the car, something the FIA believes infringes Article 3.15 of Formula One’s technical regulations, the final part of which states that ‘any car system, device or procedure which uses, or is suspected of using, driver movement as a means of altering the aerodynamic characteristics of the car is prohibited’. This clause was introduced for the 2011 season with the primary aim of outlawing F-ducts.

The FIA’s fear is that if they do not clamp down on off-throttle blown diffusers now, the systems will become more and more extreme and lead to spiralling development costs as those teams without the technology are forced to develop their own versions to remain competitive. Some commentators have also pointed out that it is probably not in the best interests of Formula One’s green credentials to have cars burning fuel when the driver isn’t even on the throttle.

As a result of the above, the FIA wants to ban off-throttle blown diffusers from next month’s Silverstone round and then outlaw blown diffusers completely for 2012, when regulations are expected to require exhaust exits be positioned at the very rear of the car.

How would the FIA police a ban on off-throttle blown diffusers?
Thanks to the fact that the FIA has access to the teams’ standardised ECU systems, the governing body can easily monitor the relevant engine mapping parameters, such as ignition, fuel and throttle levels.

Who stands to lose out most from a ban?
In theory, the teams with the most highly-developed ‘hot blowing’ systems have the most to lose, Red Bull being the most widely-cited example. However, there are differing opinions on just how much difference a ban will make. With the teams already working on revisions to engine mapping and car design in anticipation of a rule change, some feel any difference in their relative performance will be negligible. At the opposite extreme, some have suggested that with a ban in place, Silverstone could effectively herald the start of a ‘new’ 2011 championship.

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